The objective of the proposed conference is to bring together experts from academia, industry, and regulatory agencies to discuss the science involved in the policy, use, and assessment of adverse effects of atrazine. Atrazine is a triazine herbicide that kills broadleaf weeds. In the US alone, approximately 80 million pounds of atrazine are applied per year and atrazine is the number one contaminant in ground, surface, and drinking water. Several studies have suggested that atrazine induces mammary tumors, prostate cancer, and prostatitis in rodents in addition to other adverse effects on reproduction. Studies in humans suggest increases in mammary cancer in women, increases in prostate cancers in farmers and factory workers exposed to atrazine dust, and a recent study showed decreased semen quality associated with urinary metabolite levels of atrazine. Atrazine affects sex steroid hormone levels in rodents and humans in a manner consistent with hormonal mechanisms known to influence the cancers. Furthermore, a mechanism described in human cell lines, the induction of aromatase, has now been identified in amphibians, fish, and reptiles, and is consistent with the hermaphroditism observed in wildlife exposed to atrazine in the laboratory and field. The goal of the symposium is to bring together scientists from diverse fields, who might not otherwise interact in order to better understand the science underlying atrazine 's function and purported risks. Ultimately, we hope to be able to answer three questions: 1) Does the available science support the hypothesis that atrazine has adverse effects on wildlife? 2) Does the available science support the hypothesis that atrazine has adverse effects on humans and rodents? 3) Are effects on wildlife and humans and rodents consistent, i. e. are these different endpoints with common underlying mechanisms? Finally, we hope that individuals with a regulatory focus can both gain from the science discussed as well as provide guidance as to what data gaps limit regulatory action.